Iontophoretic transport of drug or biological treatments is well known and is commonly used as one way to transport such treatments across a surface and into a body. Many iontophoretic devices have been developed, as witnessed by the quantity of issued patents and pending applications mentioning such phenomena. A representative such application, titled “Rate Adjustable Drug Delivery System” filed by Birch Point Medical, Inc., was published Jul. 12, 2001 as international publication No. WO 01/49365 A1. The '49365 application is hereby incorporated by this reference as though set forth in full herein.
Existing iontophoretic devices may generally be classified into two groups based upon their electromotive source. The first such group may be characterized as disposable and is driven by a galvanic or electrochemical reaction encompassing electrodes bathed in an electrolyte carrying the treatment ions and offering a relatively low voltage. Such devices inherently require long treatment time intervals. Such devices are also generally constructed to be inexpensive, used once, and then thrown away. The second type of iontophoretic device typically is driven by an auxiliary power module. While treatment time requirements for devices having auxiliary power modules are generally reduced, the power modules are expensive and so typically must be reused.
A representative disposable device, generally indicated at 30 in FIG. 1, can be constructed on an adhesive strip 33. Cationic chamber 35 and anionic chamber 37 are formed in the adhesive strip 33 to create separated volumes in which to house cationic and anionic treatment materials, respectively. An electrolytic cell created by a chemical reaction between the cationic and anionic electrodes in an electrolyte provides the electromotive force to operate the device for ion transfer to a patient. A first electrode 39 installed in the cationic chamber 35 and a second electrode 41 installed in the anionic chamber 37 are connected by a conductor 43 to form an electron-transporting leg of an electric circuit. Application of the adhesive strip to a human body completes the circuit and initiates a flow of treatment ions through the patient's skin.
An electrode 39 may be formed from zinc, with an electrode 41 being made from silver chloride. The electrolyte contained in the cationic chamber 35 and anionic chamber 37 directly contacts the skin to be treated and necessarily is limited in reactivity to avoid skin irritation. Conductive salt solutions (such as 1% NaCl) commonly are employed as electrolytes due to their compatibility with a patient's skin. A device 30, as described, will generate an electromotive force for ion transfer totaling about 1 Volt. In use of a device 30, there is some possibility that a desired treatment chemical may undesirably interact with the electrolyte, electrode, or a product of the galvanic reaction, thereby compromising a treatment.
An alternative construction of a disposable-type device is generally indicated at 50 in FIG. 2. As a way to increase the voltage between the cationic chamber 35 and anionic chamber 37, a plurality of galvanic cells may be arranged in electrical series on an adhesive strip 33. Two such cells are illustrated in the embodiment 50. A first electrode 39 in the cationic chamber 35 is connected in series by a conductor 43 to electrode 53 in cell 55. Electrode 57, also housed in cell 55, is then connected in series by a conductor 43 to electrode 41 in cationic chamber 37. Such a two-cell arrangement can effectively double the voltage generated by the device and can therefore reduce a length of treatment time required. Additional cells may be added in series; however, the adhesive strip 33 rapidly becomes crowded, thereby limiting the practical range in electromotive force for a device 30.
FIG. 3 illustrates an exploded cross-section view through a device 30. As illustrated, the cationic chamber 35 and anionic chamber 37 typically are open toward the patient. Some sort of substrate 59 typically is provided as a receptor to hold the treatment chemicals (beneficial agent) or electrolyte in a chamber prior to installation of adhesive strip 33 onto a patient. Substrates 59 typically are made from gauze, cellulose, cotton, or other hydrophilic material. It is common practice to saturate the substrates 59 just prior to attaching an adhesive strip 33 to a patient for a treatment session. Substrates 59 may be loaded with treatment substances using a syringe or any other convenient transfer implement.
A representative device driven by a reusable auxiliary power module is illustrated generally at 60 in FIG. 4. A power module 63 typically houses sophisticated electronics and is relatively expensive (power modules are generally not regarded as single-use, disposable items). Power module 63 may provide a substantial voltage to cause ion migration through a body. Applied voltages may reach perhaps 90 Volts, although perhaps for only a very short period of time to initiate ion transfer. Depending upon the skin contact area for ion transfer from a treatment chamber and the composition of the beneficial agent, a patient may perceive a burning sensation under an applied voltage of only 30 volts. Power modules may be attached directly to an adhesive strip 33, as illustrated, but are more commonly connected in-circuit between the cationic chamber 35 and anionic chamber 37 using wires, or extension leads 65, to permit some degree of motion for a patient undergoing a treatment.
The electronics portion of a power module 63 may be constructed to generate a range of voltages, hold a voltage substantially constant for a period of time, or cause a programmable range in voltage over a period of time. Similar modulation may be made by a power module 63 to a current flowing in the circuit. However, power modules 63 represent an expense and may cause inconvenience in that operators may require special expertise to properly configure the module for a particular treatment.
A patient would benefit from a simple, disposable, iontophoretic device capable of higher voltage and more sustained current transmission than commercially available disposable devices, but being less costly than devices requiring an electronic module. An improvement in current transmission to minimize a polarization effect in commercially available disposable devices would also be an advance. A disposable iontophoretic device having a treatment time operably controlled by the working life of a disposable power source having a square-wave current flow would be an additional advance.